In Traveller, sub light speed is manifest in G's, but just how fast is a G? Is it the force required to lift said ship from Earth? then why isn't a manuver drive slower on planets? Does it automatically adjust to the size of planet you're on? Then why not go 12 Gs on a small planet? Obviously, i am either missing something, or there is a flaw in the system... Anybody care to lend an oppinion?
Just what exactly is a G?
- Thread starter endersig
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far-trader
SOC-14 10K
Morning endersig,
Just heading to bed here, just past 1am and I'm beat so hopefully if there's any errors (entirely possible) someone will point them out
Gs or gees are not a speed but an acceleration. 1G is about 9.8m per second squared. That is really "fast" compared to anything we have today or envision as probable. In CT (easiest on the tired brain
) this was rounded to a vector (a fancy word for measure of movement showing speed and direction as a line) of 10,000km per G per turn (1,000 second turns). So a ship with a 1G drive going in a straight line will cover 10,000km the first turn, 20,000km the second turn (additive) for a total of 30,000km travelled in two turns, and so on. So it's speed at the end of the first turn is about 36,000kph. If it quite accelerating at this time it would continue at a speed of 36,000kph indefinately. But our example kept accelerating and after two turns it has a speed of about 54,000kph.
Now that I've totally confused you or insulted you if you already know that on to the next question...
Most Traveller versions have a little system called contra-grav lifters. These do little else but create a field or effect that negates 99.9% of the effect of gravity on the ship. So your ship almost floats, where ever it is. This allows 1G drives to accelerate a ship at (nearly) 1G even in a high gravity field. It's magic and it makes the game easy to play while still being fairly realistic
I hope that helps without sounding condescending, it wasn't my intent if it does. Just trying (and maybe failing, please somebody check me on the above, it's late
) to answer the questions.
If I just confused anyone, ask again and maybe someone else can explain it better.
g'nite all
Just heading to bed here, just past 1am and I'm beat so hopefully if there's any errors (entirely possible) someone will point them out
Gs or gees are not a speed but an acceleration. 1G is about 9.8m per second squared. That is really "fast" compared to anything we have today or envision as probable. In CT (easiest on the tired brain
) this was rounded to a vector (a fancy word for measure of movement showing speed and direction as a line) of 10,000km per G per turn (1,000 second turns). So a ship with a 1G drive going in a straight line will cover 10,000km the first turn, 20,000km the second turn (additive) for a total of 30,000km travelled in two turns, and so on. So it's speed at the end of the first turn is about 36,000kph. If it quite accelerating at this time it would continue at a speed of 36,000kph indefinately. But our example kept accelerating and after two turns it has a speed of about 54,000kph.Now that I've totally confused you
or insulted you if you already know that on to the next question...Most Traveller versions have a little system called contra-grav lifters. These do little else but create a field or effect that negates 99.9% of the effect of gravity on the ship. So your ship almost floats, where ever it is. This allows 1G drives to accelerate a ship at (nearly) 1G even in a high gravity field. It's magic
and it makes the game easy to play while still being fairly realistic I hope that helps without sounding condescending, it wasn't my intent if it does. Just trying (and maybe failing, please somebody check me on the above, it's late
If I just confused anyone, ask again and maybe someone else can explain it better.
g'nite all
TheEngineer
SOC-14 1K
Just a good show for past 1 am
Perhaps just the addon, that the impact of local gravity on maneuver drives changes from Traveller variant to variant.
Using MT its just the way Dan presented, but at least in CT local gravity affects a ships vector, when moving close to a planet.
Regards,
Mert
Perhaps just the addon, that the impact of local gravity on maneuver drives changes from Traveller variant to variant.
Using MT its just the way Dan presented, but at least in CT local gravity affects a ships vector, when moving close to a planet.
Regards,
Mert
M
Malenfant
Guest
There's one thing I've often had trouble with, for some reason - if you're in a rocket launching vertically with an upward acceleration of 1g from the surface of a planet that has a surface gravity of 1g, what happens?
My confusion arises because to escape from a planet you need to be travelling faster than the world's escape velocity. If you fly past the planet but are travelling faster than its escape velocity then your path will be deflected by its gravity but you will not orbit the planet (your path would be hyperbolic, I think?). But whether or not you beat the escape velocity has nothing to do with acceleration at which you're travelling - you could not be accelerating at all, but if you're going fast enough you'll still be able to avoid being captured into orbit.
But if you're at the planet's surface, if you can't get an upward acceleration that is larger than the downward acceleration due to gravity, you won't be able to get off the ground (or you'll fall toward the ground if you're not far above the surface). Is that correct?
(this gets more important with gas giant refuelling. Some of the more massive gas giants have gravity at the cloudtops that is greater than 6g. Presumably a ship will not be able to 'hover' over such jovians).
My confusion arises because to escape from a planet you need to be travelling faster than the world's escape velocity. If you fly past the planet but are travelling faster than its escape velocity then your path will be deflected by its gravity but you will not orbit the planet (your path would be hyperbolic, I think?). But whether or not you beat the escape velocity has nothing to do with acceleration at which you're travelling - you could not be accelerating at all, but if you're going fast enough you'll still be able to avoid being captured into orbit.
But if you're at the planet's surface, if you can't get an upward acceleration that is larger than the downward acceleration due to gravity, you won't be able to get off the ground (or you'll fall toward the ground if you're not far above the surface). Is that correct?
(this gets more important with gas giant refuelling. Some of the more massive gas giants have gravity at the cloudtops that is greater than 6g. Presumably a ship will not be able to 'hover' over such jovians).
One thing far-trader failed to point out is that "G" in this sense is the gravity felt on earth at ground level. This is normally thought of as 9.8 m/s but it actually varies dependant on where you are (though not by a lot, the range is something like 9.5-10.0 m/s^2). For the purposes of measurement it is likely to be either 9.8 (earth average) or 10 m/s.
So no, since in this case it is used as an indicator of acceleration it isn't dependant on the planet.
One of the cute things about gravity in this case is that nothing using smooth friction can accelerate faster then the perpendicular gravitational force. ie. The most powerful car you have ever been in probably could only reach 0.5 G or so, and only certain aerodynamic designs can ever accelerate faster then 1G. Formula One class vehicles can do 2G forward acceleration at maximum . Indy cars (without those silly restrictions for safety
) can potentially acheive 4G of acceleration. These cars can break the 1G limitation by using an inverted wing to add extra downforce to the vehicle. Sorry, got distracted by shiny things.
So no, since in this case it is used as an indicator of acceleration it isn't dependant on the planet.
One of the cute things about gravity in this case is that nothing using smooth friction can accelerate faster then the perpendicular gravitational force. ie. The most powerful car you have ever been in probably could only reach 0.5 G or so, and only certain aerodynamic designs can ever accelerate faster then 1G. Formula One class vehicles can do 2G forward acceleration at maximum . Indy cars (without those silly restrictions for safety
It hangs there looking embarrassed until it runs out of fuel
Escape velocity is a descriptor of the amount of gpe that you need to exit the system. If the escape velocity is say 10km/s (a rough approximation of earths) then that is the velocity you must have at ground level to leave. For a rocket it is far easier to store the extra gpe a little at a time rather then trying to start with it. GPE is Gravitational Potential Energy, it also works the other way, a stationary rock that happens to enter the terminal pull of earth will hit the surface at arround 10km/s, a rather scary speed.
Going over the basic terms, speed is how fast you are moving, velocity is how fast you are moving in a specific direction. The difference only matters where it comes to acceleration. Acceleration is the change in velocity of the object. If that is perpendicular to the movement of the object it will start rotating, if it is from behind the velocity increases, and if it is from the front the velocity decreases.
Without contragrav no vessel would be able to leave a 6+G planet without external assistance. Contragrav cheats, and makes life far easier then it should be
By the way, MWM redefined for Traveller both the G and C.
Real world G is 9.8m/s/s
Traveller G is 10m/s/s (Bk2)
Real world C is about 310,000,000.m/s
Traveller C is 300,000,000.m/s (don't recall specific source off-hand)
Not big enough to make most issues change. But streamlines most calcs.
And Mal: those 1G ships, in MT, get explained. In MT, you can push your drives to 300%, for short periods.
Real world G is 9.8m/s/s
Traveller G is 10m/s/s (Bk2)
Real world C is about 310,000,000.m/s
Traveller C is 300,000,000.m/s (don't recall specific source off-hand)
Not big enough to make most issues change. But streamlines most calcs.
And Mal: those 1G ships, in MT, get explained. In MT, you can push your drives to 300%, for short periods.
Andrew Boulton
The Adminator
g = 9.80665 m/s^2
c = 299,792,458 m/s
http://physics.nist.gov/cuu/Constants/
10 and 300,000,000 are common simplifications; they're close enough for most uses.
c = 299,792,458 m/s
http://physics.nist.gov/cuu/Constants/
10 and 300,000,000 are common simplifications; they're close enough for most uses.
I finally found a reference for world variance of gravity. Apologies for the long load time
http://www.physics.montana.edu/demonstrations/apparatus/1_mechanics/demos/localgravitychart.html
It is a little smaller then I remembered at about +/- 0.02 m/s^2 (9.78-9.82)
http://www.physics.montana.edu/demonstrations/apparatus/1_mechanics/demos/localgravitychart.html
It is a little smaller then I remembered at about +/- 0.02 m/s^2 (9.78-9.82)
M
Malenfant
Guest
That's OK as an approximation
As others have pointed out, c is roughly equal to 300,000 km/s. I've never seen it IRL quoted as 310,000 km/s, I dunno where you got that number.
Well, either that or you launch off a world with surface gravity less than 1g
far-trader
SOC-14 10K
Or get out and pushOriginally posted by Malenfant:
Well, either that or you launch off a world with surface gravity less than 1g
(once you get clear of the 1G surface gravity you're fine 
Thanks for covering my errors guys, I see a couple points to address, maybe I'll get another moment in a while. This was too good to pass up but I gotta run.
Endersig,
A gee or G is a measure of acceleration and not a measure of speed. Acceleration is a measure of how fast speed changes.
In Traveller, a gee is 10m/s/s. (In real life it averages out ot be 9.8m/s/s.) That means with one gee you can change your speed by 10 meters per second every second.
No. A gee is also the average amount of gravitational attraction on Earth's surface. So applying one gee of thrust up will not lift you becuase Earth is pulling one gee down.
No and no. Why do you think gee would change from planet to planet? A gee is a unit of measurement, just like a meter or a second. Do meters and seconds change from planet to planet?
Huh? I don't understand that question at all.
Trust me, there is no flaw in the system with regards to gee ratings. You are definitely missing something.
Invest in a basic science book? Actually read the rules, which happen to explain this rather clearly? Go back in time and don't fall asleep in science class in school?
Sincerely,
Larsen
Note to Dr. Thomas: Re: Lifting off with 1 gee drives. In CT, contragravity lifters are implied. In MT, you can run your drives at higher ratings for brief periods of time to create escape velocities. In TNE & GURPS, contragravity lifters are explicitly mentioned. I don't remember what T4 or T20 say on the matter.
M
Malenfant
Guest
You know Larsen, there really is no need for that kind of snarkiness. If a guy doesn't know something you don't need to imply he's an idiot when you explain things to him.
Dr. Thomas,Originally posted by Malenfant:
You know Larsen, there really is no need for that kind of snarkiness. If a guy doesn't know something you don't need to imply he's an idiot when you explain things to him.
You're right, I should have simply directed him back to the rules, which, as I point out, explain what a gee is rather clearly.
I have the CT Book 2, both MT basic books, the TNE core book, and G:T in front of me as I type. All of them explain what a gee is IF you bother to read them. I'll assume T20 does the same thing too.
In his final paragraph, the original poster suggested that either the rules had an egregious flaw; which the rest of us somehow missed over the last 26 years, or that he was missing something. He then asked for our opinions.
My opinion was that the Hobby over the last 26 years had not missed such a basic detail but that he had.
Sincerely,
Larsen
M
Malenfant
Guest
I'm sure there's a lot of stuff that's "clearly explained" in the books that people continue to ask about here. Sometimes people don't have books right in front of them to check though - that's the whole point of asking questions on forums is it not?
Seems to me that he just misunderstood something, that's all - it also sounds to me like his grounding in physics isn't very high. That's not a bad thing, but I can easily see how someone unfamiliar with the term can get confused about it. Even then, there's no need to get so defensive about it that you think that he's accusing "the hobby" of failing to notice a big flaw in the details.
Seems to me that he just misunderstood something, that's all - it also sounds to me like his grounding in physics isn't very high. That's not a bad thing, but I can easily see how someone unfamiliar with the term can get confused about it. Even then, there's no need to get so defensive about it that you think that he's accusing "the hobby" of failing to notice a big flaw in the details.
TheEngineer
SOC-14 1K
Aramis, where do you get this 300% overdrive from ? SOM ?
I always thought MT is leaning on the "just ignore local gravity" model.
I always thought MT is leaning on the "just ignore local gravity" model.
Captain Zoom
SOC-9
He's getting the information from the Starship Operator's Manual put out by DGP. Without getting into alot of specifics, a ship's maneuver drive rating can be thought of a a base-line. You can exceed the rated thrust of the drive, either by a little (~40%) for a long time, or by alot (up to 400%) for very limited times, such as when landing. Of course, a badly maintained maneuver drive, an unskilled engineer, etc. can result in disaster for those who push the drive's limits.
clair_rand
SOC-9
i did wonder bout the 'overload' feature meself, never saw the SOM meself. used somethign simliar for a while.. normally closer to 200% than 300%, handwaved away as you have convection cooling of the drive plates (and maybe ram-air cooling through ducts) to handle the over heat, thus explaining why you can't do this in space.. (avoiding other problems).
as for gas giant.. always gone more for a very high speed slingshot pass through the thin atmosphere, with a decent period before you can do it again (normally while you turn round) for the hull to cool down again
as for gas giant.. always gone more for a very high speed slingshot pass through the thin atmosphere, with a decent period before you can do it again (normally while you turn round) for the hull to cool down again
